This invention relates to aircraft utilizing circulation control rotor systems, one form of which is known as X-wing aircraft, due to its feature of stoppage in flight, wherein the rotor acts as a wing.
A circulation control rotor system is described in a report entitled "Circulation Control Rotor Flight Demonstrator" by David R. Branes, Douglas G. Kirkpatrick and George A. McCoubrey presented at an American Helicopter Society Mideast Region Symposium in August, 1976. The report "Status Report on Advanced Development Program Utilizing Circulation Control Rotor Technology" by Kenneth R. Reader, Douglas G. Kirkpatrick and Robert M. Williams, Paper No. 44 presented at the Fourth European Rotorcraft and Powered Lift Aircraft Forum, Stressa, Italy, Sept. 13-15, 1978 describes an X-wing develoment program.
Davidson et al U.S. Pat. Nos. 3,319,936 and Fling et al 3,348,618 and 3,349,853 describe a control mechanism for a helicopter having circulation control with compressed air being supplied through the rotor pillar. Cheeseman et al U.S. Pat. Nos. 3,524,711 and Seed 3,567,332 describe helicopter rotors employing circulation control, as does our copending application Ser. No. 538,687, filed Oct. 31, 1983.
Our X-wing aircraft employs a rigid rotor-wing utilizing symmetrical circulation control airfoils. The rotor is driven mechanically, and lift is achieved by modulation of air circulation about the base airfoils. This is accomplished by blowing compressed air through trailing edge openings in the rotor blades, and controlling the amount of air being ejected through those openings. By cyclically modulating the amount of ejected airflow, cyclic lift control is obtained. Likewise by collectively controlling the ejected airflow collective lift control is obtained. Since forward flight in the stopped rotor mode reverses the usual orientation of leading edge to trailing edge for the blades on one side of the helicopter, provisions must be made for air circulation slots and attendant control valves for both leading and trailing edges of each blade.
The primary components for a circulation control rotor system are the rotor blades and hub, and a pneumatic system for supplying the required airflow. A mechanical collective system may be required to supplement and enhance the range of collective control resulting from the pneumatic system. It provides the necessary range of collective control required to operate over the full flight range including hover, high speed level flight and maneuver to autorotative descent. The pneumatic system is adapted to deliver compressed air separately to the leading edge and to the trailing edge of the individual rotor blades at the desired pressure and mass flow. The pneumatic system thus includes a compressor, an air storage chamber or plenum, functioning as a stationary air supply to the rotor, separate valving for controlling the flow of air to the leading edge and the trailing edge of the blades, and rotating air distribution ducts. The plenum is pressurized with air from the compressor, and a dual series of non-rotating individually actuated valves spaced in the plenum periphery control airflow and, together with compressor controls, provide tne desired air pressure and mass flow to each blade.
One reason for the lack of popularity of circulation control rotor systems is concern over a loss of plenum pressure resulting from a damaged rotor blade. The damage to a rotor blade, such as ballistic damage, can cause the entire plenum pressure to be vented through that damaged blade. The result is a loss of pneumatic control, not only of that blade, but control of all rotor blades. It is this problem, the prevention of blade pressure loss, which is solved by this invention.